Test device for detection of an analyte

ABSTRACT

A test device, system and method, the device composed of an elongated, toothbrush-shaped, transparent, plastic housing and a lateral-flow test strip for the detection of an analyte, such as a beta-lactam in milk, in the housing, the housing having an expansion cavity to receive expanded, liquid-contacted, absorbing material in the test strip, and to control lateral flow rate and times in the test strip.

BACKGROUND OF THE INVENTION

There are numerous patents and publications which describe variouslateral-flow or immunochromatographic test kits and methods for thedetection of the presence or concentration of chemical residues oranalytes or classes thereof from liquid samples. One publicationincludes "A SHORT GUIDE-Developing Immunochromatographic Test Strips" byMillipore Corporation, Bedford, Mass., while U.S. Pat. Nos. wouldinclude 4,703,017, issued Oct. 27, 1987; 5,591,645, issued Jan. 7, 1997;5,266,497, issued Nov. 30, 1993; 4,999,285, issued Mar. 12, 1991;5,238,652, issued Aug. 24, 1993; and 5,622,871, issued Aug. 22, 1997(all hereby incorporated by reference).

U.S. Pat. No. 5,622,871 describes analytical test devices for biologicalfluids which include elongated, rectangular, hollow casings to contain atest strip, and which casings have an aperture to permit visualobservation of the test results on the test strip. The casings include aprotective, removable cap to protect and enclose the application end ofthe casing. The internal constructional details of the housing are not asignificant feature of the invention, but are employed to provide ahousing for the particular test strip (column 12, lines 20-26).

It is desired to provide a new and improved analyte test device andmethod based on test strips in which the housing of the test strip isdesigned to promote the absorption, flow and efficiency of the testdevice and the tests carried out.

SUMMARY OF THE INVENTION

The invention relates to an analyte or chemical residue test device andmethod employing a lateral-flow test strip for the detection of theanalyte or residue within a housing and a method therefor.

The invention comprises an analyte test device for detecting, in thegeneral horizontal position, an analyte in a liquid sample by capillarylateral flow in an immunochromatographic test strip, which devicecomprises an elongated housing defining an elongated strip cavity havinga one open application aperture at one end and having another end, thecavity adapted to receive and hold a test strip therein, and having atransparent top cover section, to permit the observation of test resultson the test strip, the housing characterized by an enlarged applicationcavity extending outwardly from the top cover and having or adapted tohave an open end at the application end. The test device includes a teststrip positioned in the strip cavity.

The test strip comprises a support strip with a plurality of sequential,contacting, liquid-sample, permeable zones extending from the first tothe second ends, which zones permit the lateral capillary flow of theliquid sample from the first to the second end. The zones include asample-absorbing and filtering zone composed of an expandable, porous,compressed-material layer which moves, on contact with the liquidsample, between a nonexpandable state and an expandable state onabsorption of a preselected amount of the liquid sample, and a releasingzone having a mobile-phase layer thereon with a receptor for the analyteof the liquid sample thereon, typically a visible area, for example, ofcolored beads. The zones include also a reaction zone having at leastone stationary-layer analyte reference or test line, or generally a testand a separate control line thereon for observation, to detect thepresence of analytes in the liquid sample, and optionally a disposalzone of a layer of liquid-sample absorbent material for the liquidsample and to induce capillary flow to the second end. Thesample-absorbing zone with the compressed material layer is positionedadjacent the application cavity, the compressed-material layer and theapplication cavity designed to provide the compressed-material layer toabsorb a selected amount of liquid sample to be tested and sufficient tocarry out the test and to expand from a dry, nonexpandable to a wet,expanded state, and to provide for the said material layer in the wet,expanded state to fill substantially the application cavity and to causesufficient pressure on the housing walls of the expansion cavity todrive capillary flow of the liquid sample toward the disposal zone insaid strip in a selected time period and to restrict flow of the liquidsample in the application cavity to a selected volume, when the openapplication end of the test device is inserted into a liquid to obtainthe liquid sample.

In the invention, one preferred embodiment is the employment of ahousing, such as a one-piece, integral, injection-molded,all-transparent, plastic material, with the plastic material selected ordesigned to be subject to incubator temperatures of 50° C. or more forincubation times; for example, of 2 to 10-15 minutes, depending on theparticular test.

The preferred embodiment includes a generally toothbrush-type housingshape, with the enlarged, generally rectangular, toothbrush-type head atthe open application end of the housing, with a dry, inert, porous,expandable, liquid-permeable, absorbing material in a generallyrectangular layer as an absorbing zone in the test strip; for example,of cellulose or nitrocellulose, positioned beneath the open bottom ofthe application cavity or chamber. The absorbing layer on contact, suchas immersion of the application end of the housing of the test device ina liquid, will absorb a preselected amount of the liquid sample requiredfor the test. The absorbing-layer material will expand; for example, in1 to 30 seconds, to fill or substantially fill the expansion cavity andcontact the surrounding walls of the expansion-cavity housing, to causesufficient pressure within the expansion cavity and in the expandedstate of the material to drive capillary flow laterally in theunderlying test strip toward the end of the elongated housing where thetest strip is positioned. Thus, proper selection and dimensioning of theexpansion cavity and underlying absorbing-layer material which generallymimics two dimensions of the expansion cavity, permits absorbing andfiltering of the selected amount of liquid sample for the test strip,and aids in driving the lateral flow of the liquid sample in the teststrip in the housing toward the end of the test strip; for example, thedisposal zone, to receive the liquid sample where employed. If theabsorbing layer does not expand sufficiently to fill or substantiallyfill the expansion cavity, then lateral or capillary flow rates andtimes are unsatisfactory; that is, flow rate too slow and time periodtoo long. Where the absorbing layer is used in excess, then excesspressure occurs in the expansion cavity, and the expanded absorbinglayer tends to retard the desired lateral flow of the liquid sample.

The housing with the toothbrush-shaped design may comprise a separate,injection-molded housing with an optional end cover, to protect theexposed application end before sampling and after sampling, and in theincubation chamber, to prevent cross-contamination from other sources.The test device with the molded housing enables the user to handle thehandle end of the housing and to obtain a liquid sample merely bydipping the open application cavity into a liquid.

The housing also may comprise a toothbrush-shaped design, wherein theexpansion cavity is formed in a plastic, usually transparent,blister-type package which is sealed against a flat support, such as apaper strip or another plastic strip, and which encompasses within theblister package the selected test strip. The blister package includes aremovable seal strip at the one application end of the enclosed teststrip, for peeling or removal prior to use and for the introduction of aselected volume of the liquid to the application-absorbing zone of thetest strip while in the blister package. The blister package with theliquid sample and test strip may be incubated in the incubator and thetest results observed or read.

In a further embodiment, it has been discovered to be desirable toprovide one or more apertures in the housing which defines the expansioncavity, to permit the time-controlled and more rapid absorbing of theliquid sample into the absorbing material for more efficient absorptionand to reduce absorption time of the liquid sample. In particular, oneor more apertures should be placed on the top cover or surface of theexpansion-cavity housing, particularly of the molded housing, ratherthan on the sides, so that entrapped air, after immersion, will bedischarged from the expansion cavity, as the absorbing layer expandsinto the wet, absorbing, expanded state. While a flat, rectangular stripof absorbing material is shown with a generally rectangular expansioncavity which mimics and provides for the expanded, rectangular strip ofthe absorbing zone, it is recognized that the size, material, dimensionsand shape of the absorbing material and the shape or form of theexpansion cavity may vary in the practice of the invention. Typicallythe open bottom of the expansion cavity is directly above the absorbinglayer and usually of about the same width and length dimensions, topermit expansion without restriction of the absorption layer into theexpansion cavity.

While a fully transparent top cover is desirable to enclose the teststrip and observe or read the test results on the test strip, it isrecognized that the top cover may be open or have an aperture to viewthe test results, or only a section of the top cover be transparent toview the test results, or where applicable, the housing may be modified,so that the test results may be determined by optical or electronicinstrument means.

The test device may be packaged for use in a blister-type package oremploy a fixed or slidable protective cap at the application end, toprotect the test device from contamination prior to use and to protectthe test device after contact with the liquid sample and in theincubator (where required in the test), to protect againstcross-contamination. The protective cap can be removable and enclosetotally the application end of the housing, or merely be slidablyextended outwardly from the application end between a retracted useposition and extended, protective, closed position.

The test device employs a test strip selected to detect the presence orconcentration of selected analytes or residues, either a single residueor classes thereof, and visually by reference of a reaction referencezone or reference line in the test strip which may be observed ormeasured. Usually, a control zone or line is spaced apart slightlydownstream from the reference zone or lines for control purposes. Thehousing of the test device is applicable to a wide variety of presentlyemployed or described test strips which are based on lateral flow orcapillary flow, regardless of the nature of the particularanalyte-residue test, provided only that the application or liquidcontact portion of the test strip requires or uses a filtering absorbingmaterial which moves by liquid-sample contact between a nonexpanded andan expanded state at or toward the one application end of the testdevice. Typically, the test strip has a support and includes, on onesurface, a plurality of contacting, liquid-permeable, sequential zonesor sections with a stationary zone, a mobile zone and, optionally, adisposal zone. The test device is particularly useful in connection withthe liquid sample comprising a biological fluid; for example, urine;blood; or milk; and in the detection of antibiotics, like beta lactamsor toxins, viruses and the like; however, the test device may employ oneor more test strips directed to a variety of tests.

Where applicable, the test device is employed in combination with anincubator, such as a portable, electrically heated incubator with anincubation chamber which may be dimensioned to receive the test-devicehousing snugly therein for heating for a selected incubator time; forexample, 55 to 65° C., and for a period of 1 to 10-15 minutes. The testdevice and incubator also include a timer, so that the incubation periodmay be timed by a user.

In operation, the test device with a protective covering or cap has thecover or cap removed and the application end contacted with a liquid tobe tested, such as by immersion or a liquid sample pipetted into theapplication end for 1 to 10 seconds and then removed. The absorbingmaterial is allowed to expand within the expansion cavity; for example,1 to 15 seconds, then the test device placed in an incubator for a timeperiod, then removed and the test results observed or measured.

The test device and method will be described for the purposes ofillustration only in connection with certain embodiments; however, it isrecognized that various changes, additions, improvements andmodifications to the illustrated embodiments may be made by thosepersons skilled in the art, all falling within the spirit and scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective, exploded view of a molded-housing test device.

FIGS. 2, 3 and 4 are schematic, illustrative views of the use of thetest device of FIG. 1.

FIG. 5 is a perspective view of an incubator and the test device with aliquid sample.

FIG. 6 is an enlarged, front-plan view of the test strip of FIGS. 1-5,with enlarged, front, sectional views of positive and negative testresults.

FIG. 7 is a perspective, exploded view of a blister-pack test device.

FIGS. 8, 9 and 10 are schematic, illustrative, side views of the use ofthe test device of FIG. 7.

FIGS. 11 and 12 are perspective views of an incubator and the testdevice of FIG. 7 with a liquid sample.

FIG. 13 is an enlarged, front-plan view of the test strip of FIGS. 7-12,with enlarged, front, sectional views of positive and negative testresults.

FIGS. 1-13 refer to FIG. 1 and FIGS. 2-13 of the drawings.

DESCRIPTION OF THE EMBODIMENTS

In the drawings, FIGS. 1-6 show the analyte test device 10 whichincludes an elongated, molded housing 12 of a one-piece,injection-molded, transparent styrene polymer to define an elongatedcavity 14 with an open end 16, and having an enlarged, rectangularapplication cavity 18 at the one open application end of the housing 12.The housing includes an elongated bottom cavity formed during theinjection-molding process. The housing includes an optional removable,friction-fitted or snap-on protective styrene cap 22 adapted to fit overthe open application end 16 of the housing 12 and expansion apertures 19in the top cover of the application housing cavity, to increase theefficiency of expansion of the material 32 within the test time.

The housing cavity 14 includes therein on the bottom surface alateral-flow test strip 28 adapted to detect the presence of an analytein a liquid sample, such as milk. The test strip includes an elongated,adhesive, support or backing strip 30 with a plurality of sequentiallayers comprising a rectangular pad of dry, compressed, cellulosicmaterial 32 as a liquid-sample absorbent secured to the face surface ofthe support strip 30 at the one application end. The pad 32 is selectedto expand in contact with the milk, to fill the expansion cavity 18which the pad 32 mimics in two dimensions. For example, with milk, thepad would be about 3-4 mm by 12-14 mm, while the cavity 18 would beabout 5-6 mm by 15-16 mm by 4-6 mm in height. The expansion cavity maybe dimensioned to be about 60% to 30% less than the full expansion ofthe sponge material.

The support strip 30 includes a treated, mobile-phase, support layer 33with a visible receptor-probe area 34, a stationary-phase layer 36 whichincludes a reference line 38 and a control line 60 for the analyte to bedetected, and a cellulosic absorbent pad 40 at the distal end of thesupport strip 30 to capture excess liquid sample. The housing 12includes a transparent top cover 42 for visual observation of thereference line 38 and control line 40. The test strip 28 is placed andpositioned loosely in the elongated cavity 14, with the pad 32positioned beneath the expansion cavity 18, and the pad extendinggenerally to about or slightly beyond the plane of the open applicationend, and the end covered prior to use by the protective cap 22.

In operation, the cap 22 is removed prior to use and the openapplication end of the housing 12 inserted briefly (1 to 10 seconds) inthe liquid; for example, milk, to be tested employing the elongatedhousing 12 as a handle (see FIG. 2). The test device 10 is removed andthe pad 32 allowed to expand to fill the expansion cavity 18 and tostart the lateral flow of the milk sample through the test strip 28 (2to 6 minutes) (see FIGS. 3 and 4). Preferably, cap 22 is inserted toprotect against cross-contamination, and the test device then placed ina horizontal position, with the application cavity 18 extendingdownwardly in an electric-heated incubator 46 with a cavity 47 shaped toreceive the test device, and incubation carried out; for example, 1 to 8minutes,the incubation temperature observed through thetemperature-indicator scale 48 (see FIG. 5). The incubated test device10 is then removed and reversed, and the front view of the test devicewith reference line 38 and control line 40 observed (see FIG. 6). Theline readings for positive and negative controls are illustrated in FIG.6 adjacent the front view of the test device 10. In the sponge material32, expansion is controlled by the expansion cavity 18 volume and size,resulting in the sponge material 32 completely filling the cavity 18with a preselected volume of liquid; for example, 0.1 to 1.0 ml, so theamount of liquid sample taken in for the test is controlled to thecorrect amount. The dimensions of the expansion cavity 18 prevent thesponge material 32 from full expansion, so that pressure is maintainedin the expanded sponge (see FIG. 4) to aid in forcing capillary-lateralflow of the liquid sample through the test strip 28 in the housing 12.

The drawings in FIGS. 7-13 illustrate a further embodiment of the testdevice 50 in a transparent blister package which includes atransparent-tape plastic seal strip 52 with a peel tag 54 at one end,and a transparent blister package 56 adhesively secured to the strip 52,to enclose a test strip 28 therein. The blister package 56 includes anelongated cavity 68 to hold strip 28 and an expansion cavity-housing 58at the one end to form a generally toothbrush-shaped cavity within theplastic blister package 56 and strip 52. The selected test strip 28 issealed and enclosed within the transparent blister package.

FIG. 8 shows a side sectional view of the blister-package test device 50prior to use. FIG. 9 shows the blister-package test device 50 with oneend peeled back by peel tab 54, to expose the expansion housing cavity58 and the dry filter-absorbent sponge pad 32 of the test strip 28, sothat a defined amount of a liquid sample can be added; for example, bypipet, as shown. FIG. 10 illustrates the test device 50 after additionof the liquid sample, and with the peel tab resealed and with the spongepad 32 fully expanded by the liquid sample within housing cavity 58 andready to incubate.

FIG. 11 illustrates the test device 50 upside down and placed in one oftwo cavities 47 in an incubator 46. FIG.12 illustrates the technique ofadding the liquid sample (see FIG. 9) with pipet, while the peel tab 54is pulled away from the end of the test device 50 in the incubator, thetest device sealed (see FIG. 10) and incubated. The test results of thecompleted test may then be read through the transparent top cover ofblister package 56, as shown in FIG. 13, to provide positive or negativetest results.

The test; for example, the inhibition assay test, strip 28, selected forbeta lactams in milk, is a quick test for beta lactams in comingled rawand pasteurized milk. In operation, the incubator 46 temperature gauge48 is checked to ensure an incubator temperature of 55° C.; for example,temperature indicator 48 may be colored; for example, green, for use.The test device 50 is placed on one of the incubator 46 cavities 47,with the flat side facing up and the peel tab 54 peeled back far enoughto expose the sponge pad 32; for example, 1/2 of an inch. The milk to betested is mixed thoroughly before testing, and about 0.5 ml added bypipet to the exposed sponge pad 32 and the adhesive tape tab 54 resealedby hand pressure, and the incubator 46 cover closed. The test device 50is incubated, for example, at least 6 to 8 minutes and then removed fromthe incubator 46 and held vertically and a comparison made within about1 hour between the test or reference line 38 with the control line 40.If no control line 40 appears, the test is invalid. A negative test iswhen the reference line 38 is the same or darker than the control line40. A positive test is indicated when the test or reference line 38 isabsent or clearly lighter than the control line 40.

In more detail, the test device 10 capable of detecting analytes inbiological fluids comprises the following components:

a). A compressed material 32, such as cellulose, that is capable ofabsorbing said biological fluid and acting as a prefilter to removecoarse contaminants, such as hair, dirt, etc. Said compressed material,32 is sized to absorb a fixed amount of sample required to complete theassay. This compressed material, when expanded and contacting the insidewall of housing 12, causes sufficient pressure to drive capillary flowalong the components 32 and 36 in the time required (3 to 8 minutes) fora marketable test. Said component (32) overlaps said component 32 1 to10 mm such that, when an aqueous sample, such as milk, is added tocomponent 36, the sample will flow onto said component 32.

b). A housing 12 for said components 36, (32), 30, 32, 33, 34, 36, 38,and 40. A housing should be used to allow for addition of biologicalsample, either by dipping, pouring or pipetting. Said housing isconstructed of either a flexible or hard material, such as polystyrene,polypropylene, or polyethylene.

c). A mobile-phase support pad 33 made of polyester, polyethylene orglass fiber that acts as a secondary filter for removal of less coarsematerials (somatic cells). The support has been pretreated with achemical solution, such as 0.01 to 0.2 M sodium citrate pH 6-8, capableof neutralizing interferences found in biological samples. Themobile-phase support pad 33 overlaps said component 36 by 1 to 4 mm.

d). A mobile phase 34 comprising:

i) highly specific binding proteins or monoclonal antibodies capable ofbinding to an analyte and titrated to a known concentration to makeunavailable for further reaction/detection a known amount of analyte.This unavailability for further reaction/detection allows for theadjustment of a detection level of one or more analytes to a specifiedlevel of concern. For example, in ceftiofur, a beta-lactam with atolerance level of 50 ppb in milk, sensitivity can be changed from 5 ppbto between 40-50 ppb by the addition of a monoclonal antibody specificfor ceftiofur. The specific monoclonal antibody removes a specificanalyte from binding to a receptor or antibody which is capable ofbinding a family of related compounds and;

ii) highly purified proteins; for example, beta-lactam receptor oranti-tet lgG, prepared by affinity purification and/or a combination ofhydrophobic/ion-exchange HPLC which are then attached to a colored,fluorescent, or infrared probe 34 which can be observed byoptical/instrumental means or both. Attachment of proteins to a probe iscalled binding protein/probe complex; and

iii) the mobile phase is sprayed, using a machine by Ivek, Biodot, orCamag, or absorbed onto pad 33 in a solution containing 5 to 20% sugar,such as sucrose or trehalose, 5 to 20% protein, such as BSA orPrimatone, 5 to 100 mm of a buffer solution (phosphate or Trizma base)with a final pH of between 6-8. The mobile phase is sprayed on the upperportion of the mobile-phase support pad 33, such that component (32)does not overlap portion of said component 32, but rather said component32 overlaps said component 33 by placing the topmost portion of saidcomponent 32 1 to 7 mm before the sprayed portion of said component(32). A stationary phase membrane 36 consisting of nitrocellulose ornylon which has multiple reaction zones present and comprising:

capture zone(s) is/are formed by spraying in a test line form 38 using aspraying instrument, such as Ivek, Biodot or Camag. The purpose of saidcapture zone is to capture unreacted binding protein/probe complex forviewing or measurement. Capture zone(s) consist of an analyte ofdetection; that is, penicillin G or a member of said analyte family;that is, beta-lactams, coupled to a carrier protein; that is, BSA, IgG,KLH, suspended in a 5 to 100 mm buffer solution (phosphate or Trizmabase) at a pH range of 6-8. Total protein concentration of the antibodysolution ranges from 0.2 to 100 mg/ml and;

a control zone is formed by spraying in a line form 40 using a sprayinginstrument, such as Ivek, Biodot or Camag. The purpose of said controlzone is to capture binding protein/probe complex that has not bound tosaid capture zone(s). The control zone consists of an antibody specificto the binding protein/probe suspended in 5 to 100 mm of a buffersolution (phosphate or Trizma) at a pH range of 6 to 8. Total proteinconcentration of antibody solution ranges from 0.2 to 100 mg/ml.

A comparison of the control zone 40 to the capture zone(s) 38 yieldstest result. Typically, if the control zone is darker than the capturezone(s), analyte is present at detection level or greater (see FIG. 6and FIG. 13).

A plastic backing 30 with adhesive is employed for the mounting of zones32, 36 and 40.

A disposal pad 60 made of pressed cellulose or other absorbent materialis employed to keep the sample flow consistent and to retain the reactedsample. The disposal pad overlaps the stationary-phase membrane 36 by 1to 5 mm.

An aqueous biological sample is added to component 32 of a test device10. Component 32 serves as a sample pad which expands as it absorbs thesample. Component 32 overlaps component 33, and the fluid flows onto themobile-phase support where the mobile-phase materials dissolve into thebiological fluid. Analytes present in the sample begin binding with thespecific binding protein(s) 34 attached to the probe. At the same time,specific unbound antibodies or binding proteins will bind with specificanalytes to adjust their sensitivity to the test. The mobile-phasesupport pad 33 overlaps the stationary-phase membrane E(36), and thebiological fluid, along with the mobile-phase materials 34, continue toreact as all flow up the stationary phase. When the bindingprotein/probe complex reaches the capture zone, a portion of the bindingprotein/probe complex will bind to the capture zone. In a positivesample, analyte in the sample will have bound to the bindingprotein/probe complex, reducing the amount of binding protein/probecomplex capable of binding to the capture zone. When the materialreaches the control zone, a portion of binding protein/probe complexwill bind the control zone. Excess reagent is then absorbed into thedisposal pad.

In a negative sample, reagents are titrated, so that the capture zonewill have the same or preferably a greater amount of the probe bindingto it than in the control zone. Conversely, in a positive sample, thecontrol zone will have a greater amount of the probe binding to it thanthe capture zone.

In one manifestation of this test device 10, a beta-lactam test is madeto assay for beta-lactams in milk at a safe level. A partially purifiedbeta-lactam receptor from BST (Bacillus stearothermophilus) is bound toa colloidal gold sol to make a beta-lactam binding protein/gold beadprobe 34. This is sprayed onto the mobile-phase support along withmonoclonal antibodies to ceftiofur and cephapirin, to reduce thesensitivity of these two antibiotics to a safe level. To the captureline 38 is sprayed a ceforanide-BSA conjugate, and to the control line40 is sprayed an antibody to the BST beta-lactam receptor. A raw-milksample (0.5 ml) is applied to the sample pad 32 by pipette in testdevice 50 or dripping the open end 16 of housing 12 in test device 10,and the test strip 28 is incubated at 55° C. After 8 minutes, the teststrip is removed from the incubator 46 and analyzed. If the capture(test) line 38 is darker or the same color as the control line, thesample 40 is negative, and, if the capture line is lighter than thecontrol line, the sample is positive.

Test results are as follows:

                  TABLE 1                                                         ______________________________________                                        Beta-lactarn assay in milk using latcral flow test device.                      Number of assays                                                                             sample        result                                         ______________________________________                                        30           zero control   allnegative                                         10               penicillin G at 5 ppb  all positive                          10              penicillin G at 4 ppb 5 positive, 5 negative                  10   penicillin G at 3 ppb 3 positive, 7 negative                             10               ampicillin at 6 ppb all positive                             10               ampicillin at 4 ppb all positive                             10               ampicillin at 3 ppb  5 positive, 5 negative                  10              amoxicillin at 6 ppb all positivc                             10              amoxiclllin at 4 ppb 8 positive, 2 negative                   10               amoxicillin at 3 ppb 4 positive, 6 negative                  10              ceftiofur at 30 ppb 3 positive, 7 negative                    10              ceftiofur at 40 ppb 8 positive, 2 negative                    10               ceftiofur at 50 ppb  10 positive                             10               cephapirin at 12 ppb  2 positive, 8 negative                 10               cephapirin at 15 ppb  5 positive, 5 negative                 10              cephapirin at 20 ppb  9 positive, 1 negative                ______________________________________                                    

The described test is an inhibition-type assay. Analyte in the samplebinds with a beta-lactam binding protein/gold bead probe and inhibitsbinding to a stationary beta-lactam bound to the surface of themembrane. Addition of a specific monoclonal antibody to ceftiofur hasaltered its inhibition level from approximately 5 ppb to between 40 and50 ppb. Addition of a specific monoclonal antibody to cephapirin hasreduced its sensitivity from approximately 3 ppb to between 15 to 10ppb.

The test device of the invention may be used with test strips fordetecting a variety of analytes, such as toxins like alfatoxins; as wellas beta-lactams like penicillin, ampicillin, amoxicillin, cloxacillin,dicloxacillin, oxacillin, ceftiofur, and cephapirin; tetracyclines likechlortetracycline, oxytetracycline and tetracycline; sulfoanamides likesulfadimidine, sulfadimethoxine, sulfamerazine, sulfathiazole andsulfadiazine; macrolides like erythromycin, spiramycin and tylosin;aminoglycocides like gentamicin, neomycin and DH/streptomycin; andothers like dipsone, chloramphenicol, novobiocin, spectinomhcin andtrimethoprim, to detect the maximum residue-analyte limits in thesample.

What is claimed is:
 1. An analyte test device for the detection of ananalyte or analyte class, which test device comprises:a) a test devicehousing having two ends, walls to define an elongated strip cavity, andan expansion cavity at one end of the strip cavity; b) a lateral,capillary-flow, elongated test strip having two ends located within thestrip cavity and designed for the detection of an analyte or analyteclass from a liquid sample; the test strip includes, at a first end, aliquid sample-absorbing material and a reaction-detection materialtoward a second end; wherein the liquid sample-absorbing material islocated within the expansion cavity; c) the liquid sample-absorbingmaterial of selected dimensions and moves within the expansion cavitybetween a dry, nonexpanded state and a wet, expanded state whencontacted with the liquid sample; d) the expansion cavity selected indimensions to mimic generally the width and length of the liquidsample-absorbing material and to permit expansion of the liquidsample-absorbing material to the wet, expanded state within theexpansion cavity, and into contact with at least one wall of the housingto control the volume of the liquid test sample absorbed, and to providesufficient pressure to drive capillary flow of the absorbed liquidsample, in a selected time period from the first end toward the secondend of the test strip; e) a means to introduce the liquid sample intocontact with the liquid sample-absorbing material; and f) a means for auser to determine the detected analyte or analyte class.
 2. The testdevice of claim 1 wherein the housing includes an aperture in theexpansion cavity to reduce absorption time of the liquid sample by thedischarge of entrapped air.
 3. The test device of claim 1 wherein theaperture is located on a top housing wall of the expansion cavity. 4.The test device of claim 1 wherein the housing comprises a flat-sealstrip and a transparent plastic housing secured to the seal strip. 5.The test device of claim 4 wherein the flat seal strip includes,adjacent the expansion cavity, a resealable peel strip to allow theintroduction of the liquid sample into contact with the liquid-absorbingmaterial.
 6. The test device of claim 5 wherein the resealable peelstrip further includes a peel tab at the one end of the flat-seal strip,the peel tab facilitates the movement of the resealable peel stripbetween a peeled state wherein a liquid sample may be placed in contactwith the liquid sample-absorbing material, a sealed state, and aresealed state against the seal strip.
 7. The test device of claim 1wherein the means to determine the detected analyte or analyte classincludes a transparent, top housing.
 8. The test device of claim 1wherein the housing comprises a transparent, molded plastic housing. 9.The test device of claim 8 which includes a removable cap to cover anopen end of the housing.
 10. The test device of claim 1 wherein thehousing includes a top wall of selected height in the expansion cavityto prevent the full height expansion of the liquid sample-absorbingmaterial in the wet, expanded state.
 11. The test device of claim 1wherein the liquid sample-absorbing material is designed to receive andretain a liquid sample of about 0.1 to 1.0 ml.
 12. The test device ofclaim 1 wherein the liquid sample-absorbing material is designed toabsorb a liquid sample in about 1 to 30 seconds.
 13. The test device ofclaim 1 wherein the liquid sample-absorbing material comprises a dry,compressed cellulosic material.
 14. The test device of claim 1 whereinthe test strip is selected for the detection of an antibiotic analyte ortoxic analyte or analyte class.
 15. The test device of claim 1 whereinthe reaction-detection material includes a reference line and a controlline, and the analyte or analyte class is detected by a change in colorof the reference line, or control line, or both lines.
 16. The testdevice of claim 1 wherein the liquid sample-absorbing material comprisesa generally rectangular layer and in the wet, expanded state, contacts ahousing top wall of the expansion cavity.
 17. The test device of claim 1wherein the test strip comprises:a) a support strip with a plurality ofsequential, contacting, liquid sample-permeable layers extending fromthe one end to the other end, which layers permit the lateralcapillary-flow of the liquid sample from the one end to the other end,and which layers include:i) a liquid sample-absorbing material layercomposed of an expandable, porous, dry, compressed material; ii) areleasing material layer having a mobile-phase thereon with a receptorfor the analyte or analyte class of the liquid sample thereon; iii) areaction-detection material layer having at least one analyte referenceline and a spaced-apart control line thereon for observation to detectthe presence or absence of an analyte or analyte class in the liquidsample, by a change in color; and iv) optionally, a disposable liquidsample-absorbent material layer for the liquid sample, to inducecapillary flow to the second end.
 18. The test device of claim 1 whereinthe expansion cavity is dimensional to be about 30 to 60 percent lessthan the wet, expanded state of the liquid-sample absorbing material.19. The test device of claim 1 wherein the liquid sample-absorbingmaterial has width and height dimensions of about 3 mm by 14 mm, and theexpansion cavity has dimensions of about 5 mm by 16 mm in width andlength, and about 4 to 6 mm in height.
 20. An analyte test device forthe detection of an analyte or analyte class, which test devicecomprises:a) a housing which comprises a transparent plastic blistersecured on a flat seal-backed strip, the housing having two ends, wallsto define an elongated strip cavity, and generally is rectangular inwidth and length, and a selected height expansion cavity with a tophousing wall at one end of the strip cavity; b) a lateral,capillary-flow, elongated test strip having two ends and located withinthe strip cavity and designed for the detection of an analyte or analyteclass from a liquid sample, the test strip includes, at a first end, aliquid sample-absorbing material and a reaction-detection material; thetest strip further includes a reference line and a control line toward asecond end to detect an analyte or analyte class; wherein, the liquidsample-absorbing material is located within the expansion cavity; c) theliquid sample-absorbing material of selected dimensions and moves withinthe expansion cavity between a dry, nonexpanded state and a wet,expanded state when contacted with the liquid sample; d) the expansioncavity is selected to permit expansion of the liquid sample-absorbingmaterial in the wet, expanded state into contact with the top housingwall, and to provide sufficient pressure to drive the capillary-flow ofthe absorbed liquid sample, at a selected flow rate, from the first endtoward the second end of the test strip; and e) an adhesive peel stripat the one end of the housing, which peel strip moves between a sealedstate to seal the expansion cavity, an unsealed state wherein a liquidsample may be introduced into the expansion cavity, and a resealed stateto seal the expansion cavity containing the absorbed liquid sample.